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Use a 555 timer as a switch-mode power supply. (design ideas).
- Article from:
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EDN
- Article date:
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November 14, 2002
- Author:
- Lager, Aaron
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Copyright informationCOPYRIGHT 2002 Reed Business Information. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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MOST SWITCH-MODE power supplies rely on a PWM (pulse-width-modulated) output that is controlled via voltage feedback. A 555-timer IC can inexpensively perform PWM. The circuit in Figure 1 shows how to turn a 555 PWM circuit into an switch-mode power supply with only one simple equation. The design uses two 555s. I[C.sub.1], in astable mode, triggers I[C.sub.2] in PWM mode. I[C.sub.1] is set to oscillate at approximately 60 kHz at a high duty cycle. The output is low for only approximately 2.5 [micro]sec to trigger the PWM circuit and then goes high for the rest of the period. The PWM circuit has a maximum pulse width of approximately 85 [micro]sec, and it becomes shorter, ...