04t

If it is expressed in square centimeters, divide this last relation by 6.45. Then where P0 is in watts for J5max in gauss, Ae and Ab are in square centimeters, f is in hertz, and Dczna is in circular mils per rms ampere. This result specifically, that the available power from a given core in a push-pull topology is twice that for the same core in a forward converter topology could have been quite easily foreseen. In the push-pull, each transformer half must...

2500

Figure 6.5 Anode-to-cathode voltage fall time. Marconi ASCR type ACR25U characteristics. flow at an anode voltage in the vicinity of 25 V and dissipation would be high. Figure 6.5 also shows that if anode current pulses are half sinusoid, their base width should be longer than 2.5 xs to avoid an on anode potential greater than 5 V throughout the entire half sinusoid. Figures. 6.6 and 6.7 show maximum dV dt and tq for the Marconi ACR25U. 6.3 SCR Turnoff by Resonant Sinusoidal Anode Currents...

WQ 1 Vlcp

From Figs. 13.6 and 13.7, some of the problems with resonant converters can be seen. 13.4.3 Regulation with series-loaded half bridge in continuous-conduction mode (CCM) For a number of reasons, Steigerwald states that operating above the resonant peak (ARM) is preferable to below resonance. Figure 13.6 shows how the continuous conduction mode SRC half bridge regulates. If initial operation were at A at Q 2 at normalized frequency 1.3, the output input voltage ratio would be 0.6. Now if the...

T

Figure 2.4 (a) Current in transformer center tap. Equal volt-second product on both halves of transformer primaiy. (b) Transformer center tap current. Unequal volt-second product on both halves of transformer primary. Core is not yet on curved part of hysteresis loop, (c) Transformer center tap current. Unequal volt-second product. Upward concavity indicates dangerous situation. Core is far up on curved part of hysteresis loop, id) Adding a diode in series with one side of primaiy to test how...

Current Mode and Current Fed Topologies

Current-mode1-7 and current-fed9-20 topologies are grouped into one family despite their very significant differences. They are grouped together because they gain advantages by controlling both input current (although in different ways) and output voltage. Current mode (Fig. 5.3) has two feedback loops an outer one which senses DC output voltage and delivers a DC control voltage to an inner loop which senses peak power transistor currents and keeps them constant on a pulse-by-pulse basis. The...

132 Resonant Forward Converter

First the simplest resonant circuit, the resonant forward converter will be discussed primarily to see how it is arranged for transistor turnoff to occur at zero current and to see how critical the exact turnoff time may be. Figure 13.1 shows a simple resonant forward converter3 operating in the discontinuous mode. Discontinuous mode implies that current in the resonant LC circuit is not a continuous sine wave, but a sequence of a burst of one half or one full cycle of sine-wave current...

Uc3854 Schematic Diagram

Uc3854 Using Pfc Circuit

Figure 15.6 Regulation against load current changes in a continuous conduction mode boost converter. Figure 15.6 Regulation against load current changes in a continuous conduction mode boost converter. which is the previously mentioned Eq. 15.1. Now in Fig. 15.5a, output voltage regulation is achieved by chang ing Ton in accordance with Eq. 15.1 as Vin changes. This is done with the pulse width modulator (Fig. 15.5a). If Vin momentarily changes, so does Vo. A fraction of Vo ( Vea in) is sensed...

Half and Full Bridge Converter Topologies

Half- and full-bridge topologies subject their transistors in the off state to a voltage stress equal to the DC input voltage and not to twice that as do the push-pull, single-ended, and interleaved forward converter topologies. Thus the bridge topologies are used mainly in offline converters where twice the rectified DC would be more than the usual switching transistors could safely tolerate. Bridge topologies hence are almost always used where the nominal AC input voltage is 220 V or higher...

Is Lt1170 Substitute For Lt1070

* Package Options DIP Dual-ln-Line Package, SO Small Outline, SSOP Shrink Small-Outline Package, TO_ Can ** Temperature Ranges C 0 C to +70 C, E 40 C to +85 C, M -558C to +125 C t Prices provided are for design guidance and are POB USA. International prices will differ due to local duties, taxes, and exchange rates, tt Future product contact factory for pricing and availability. Specifications are preliminary. manufacturers' devices. This discrepancy is due only to the author's earlier...

334

And since the maximum duty cycle of this peak SCR current is tj 2i (min> 0.25 (Fig. 6.13a and 6.13c), the SCR rms current is Jrms(scR) 64.7 x V 25 V2 22.9 A. This is easily within 40 peak rms capability of the Marconi ACR25U. Also, as assumed above, the antiparallel diode peak current is one-fourth of the SCR current or 64.7 4 16.2 A. With a 1.62 turns ratio, the peak rectifier diode currents will be 104.8 and 26.2 A corresponding to the peak SCR and antiparallel diode currents. With such...

72

Figure 17.6 Power switch on voltage, LT1170 boost regulator. It is the on dissipation (VonIonTon T) rather than the peak current rating which determines how much peak current may be drawn. Attempting to operate at the device peak current rating may result in requiring a heat sink very much greater than the device package itself. Figure 17.6 Power switch on voltage, LT1170 boost regulator. It is the on dissipation (VonIonTon T) rather than the peak current rating which determines how much peak...

2420

704 0.070 0.022 0.002 0.0 0.1 0.1 0.2 0.2 0.4 0.5 0.6 0.7 0.07 905 0.101 0.034 0.003 0.1 0.1 0.3 0.4 0.5 0.8 1.1 1.4 1.6 0.13 1107 0.167 0.054 0.009 0.3 0.3 0.7 1.0 1.4 2.2 2.9 3.6 4.3 0.25 table 7.2a Maximum Available Ouput Power in Forward Converter Topology Continued Output power in watts at T 7 , _ _Volume, Core Ae, cm2 Ab, cm2 A,Ab, cm4 20 kHz 24 kHz 48 kHz 72 kHz 96 kHz 150 kHz 200 kHz 250 kHz 300 kHz cm3 Pot Cores, Ferroxcube-Philips continued 0.9 1.9 2.8 3.7 3.1 6.2 9.3 12.4 7.2 14.5...

02

01.02 Q1.Q2 Q1, Q2 Q1, Q2 Figure 2.13 Double-ended forward converter. Transistors Q1 and Q2 are turned on and off simultaneously. Diodes Dl and D2 keep the maximum off voltage stress on Ql, Q2 at a maximum of Vdc as contrasted with 2Vdc plus a leakage spike for the single-ended forward converter of Fig. 2.10. Although there are a number of bipolar transistors with Vccv ratings up to 650 and even 850 V which can take that stress, it is a far more reliable design to use the double-ended forward...

1 2 4 6 1 2 4 6

Allied calls its product Metglas 2714A. Toshiba has two amorphous core materials MA and MB. Toshiba MB material is closely identical to Metglas 2714A in core losses, coercive force and squareness of its hysteresis loop. Toshiba MA material is midway between Vfe-mil Permalloy and MB material. Metglas 2714A material is also used by Magnetics Inc. for magnetic amplifier cores in its own line of standard-sized cores. Curves of core loss versus peak flux density at various frequencies

DB lJL gauss118

Thus, as shown in Fig. 1.12, if a core is subjected to a positive flux change of dB B2 - Bl, when, say, the dot end of the winding had been positive, the core must be restored exactly to B1 by a reversed voltage polarity before original polarity voltage may be applied. If not, Figure 1.12 Setting and resetting a magnetic core. A core must not be allowed to walk up or down its hysteresis loop. If it is driven from, say, Bl to B2 by a given volt-second product, it must be subjected to an equal...

409 412

Turnon, Turnoff Switching Losses and Snubbers 413 11.2 Transistor Turnoff Losses without a Snubber 414 11.3 RCD Turnoff Snubber Operation 416 11.4 Selection of Capacitor Size in RCD Snubber 418 11.5 Design Example RCD Snubber 419 11.5.1 RCD snubber returned to positive supply rail 420 11.6 Nondissipative Snubbers 421 11.7 Snubber Reduciton of Leakage Inductance Spike to Avoid 11.8 Transformer-Aided Snubber 425 References 426 Chapter 12. Feedback-Loop Stabilization 427 12.2 Mechanism...

Info

Stricted to the nonoverlapping mode, it is seen that the design for overlapping and crossing into nonoverlapping mode permits a larger range of DC input voltages and allows a larger on time at high input voltages. This latter permits the use of bipolar transistors, which would have difficulty operating reliably at the low on times close to the vicinity of their storage times. 5.6.7.13 Voltages, currents, and wire size selection for design example in overlap mode. Transistor currents and...

E2

T Always connect E1 to the ground pin on minidip, 8-and 16-pin surface mount packages E1 and E2 internally tied to ground on T03 and T0220 packages. Power transistor on time Vc Error amp output threshold voltage Figure 17.2 a LT1170 100-kHz, 5-A boost regulator 6 LT1170 boost regulator waveforms. This is a classical current-mode boost regulator. Output transistor on time is initiated by the clock pulse. It is terminated when the ramp-on-a-step voltage waveform across sensing resistor Rs crosses...

Bj

Figure 10.16 The BH loop operating locus of magnetic-amplifier cores Fig. 10.15 . As core MIA moves from B0 to BS, core M1B is pushed down from Ba to B0. Time to move from B0 to Bs is the on time of the power transistors. On time is determined by how far down from Bs the initial starting ping fl0 has been pushed. This is determined by the DC current in control winding iVc, which is proportional to the output voltage Fig. 10.15 . next half period the sequence reverses M1B is driven up from B0 to...

300

For flux excursions between positive and negative saturation, tl W cm3 at 25 kHz. For flux excursions between positive and negative saturation, tl W cm3 at 25 kHz. which had been cast aside 30 years ago. But the Royer, operated in the current-fed mode, with small collector-to-opposite-base flipover capacitors and with the new low-loss amorphous cores is very attractive in many applications. If line regulation is not required, it is extremely low in parts count Figs. 6.23, 6.24 . Its major...

862

Drain currents and drain-to-source voltage at 30 above maximum specified output power Drain currents and drain-to-source voltage at 30 above maximum specified output power Showing ringing during dead time when RC snubbers R4, C4 and C5 are removed from primary Figure 14.17 Ringing at drain during transistor dead time. Showing ringing during dead time when RC snubbers R4, C4 and C5 are removed from primary Figure 14.17 Ringing at drain during transistor dead time. sorbed and subsequently...

1

If the wire size is chosen on the basis of 500 circular mils per rms ampere, the required number of circular mils is 500 x 1.97P Circular mils needed - 2.3.10.5 Secondary rms current and wire size selection. It is seen in Fig. 2.11 that the secondary current has the characteristic shape of a ramp on a step. The pulse amplitude at the center of the ramp is equal to the DC output current. Thus the equivalent flat-topped secondary current pulse at vdc when its width is a maximum has an amplitude...

116 Nondissipative Snubbers18

The conventional RCD snubber most often ends up dissipating 10 W or more for off-line switching supplies operating at over 50 kHz. This is troublesome not only for the added dissipation but also because of the size and required location of the snubber resistor. General practice is to derate power resistors by a factor of 2 and thus 10 W of dissipation usually requires the use of a 20-W resistor. A 20-W resistor is quite large, and finding a location for it is often difficult. Also, in...

Miscellaneous Topologies

6.1 SCR Resonant Topologies Introduction The silicon controlled rectifier SCR has been used in DC AC inverters and DC DC power supplies for over 25 years.1,2 It is available with higher voltage and current ratings at lower cost than bipolar single or Darlington types or MOSFET transistors. Because of the higher voltage-current ratings, it is used primarily for supplies of over 1000 W. It will be recalled that an SCR is a solid-state switch which is easily turned on by a narrow pulse at its...

V

And selecting CQ from the average value of the R0C0 product, which is closely 65 x 106 or The preceding result that the output ripple is determined mainly by the ESR of the filter capacitor Ra has been demonstrated more generally in a paper by K. V. Kantak.1 There the author shows that if R0Ca is is larger than half the transistor on time and half the transistor off time which is the usual case the output ripple is determined by the ESR resistor itself as demonstrated above for a particular...

Topologies

Fundamental Switching Regulators Buck, Boost, 1.2 Linear Regulators Swtiching Regulator Ancestors 4 1.2.1 Basic operation merits and drawbacks 4 1.2.2 Linear regulator drawbacks 5 1.2.3 Power dissipation in the series-pass transistor 5 1.2.4 Linear regulator efficiency versus output voltage 6 1.2.5 Linear regulators with PNP series-pass transistors 1.3 Buck Switching Regulator Topology 9 1.3.2 Significant current waveforms in buck regulator 12 1.3.3 Buck regulator efficiency...