Hi, could you point me to a push-pull circuit for power boost?  I have
an immediate need for this!  What I tried worked for high side (PNP) and
low side (NPN) separately, but when run together there was massive
current thru them due to having them simultaneously switch.  I have only
a squarewave clock as a source - not a PIC.

Do they need to be biased to avoid being (semi) on simultaneously?  Or
are two separate nonoverlapping clocks required?

Thanks ...
Jesse



Michael Rigby-Jones wrote:
>>-----Original Message-----
>>From: Tal [SMTP:tal@ZAPTA.COM]
>>Sent: Thursday, May 01, 2003 5:45 PM
>>To:   PICLIST@MITVMA.MIT.EDU
>>Subject:      [PIC]:[EE]: How to build a cheap charge pump
>>
>>Hello,
>>
>>I am looking for a cost sensitive (that is, cheap in very high volume
>>manufacturing) DC/DC converter to create a low current, not regulated
>>bias voltage in a circuit that already contains a PIC.
>>
>>The circuit should output 11 to 17 VDC, non reugulated and load current
>>of no more than 3 to 5ma. The PIC is running on 4 to 5VDC but an higher
>>voltage of 5 to 6 volt may also be available in the circuit.
>>
>>The circuit can use PIC outputs if needed (e.g. a continious square wave
>>from a PWM) but should not require continious software operation since
>>the PIC is already running a tight timing software.
>>
>>Any help/ideas/pointers will be greatly appreciated.
>>
>
> Using a classic voltage multiplier ladder from the PWM output may not be
> very satisfactory in this case.  You reqire 11-17 volts at a maximum of 5mA.
> This would require at least a voltage trippler.  The current drawn from the
> PIC is going to be an average of three times your 5mA, but the peak current
> will be higher, likely above the 20mA pin limit.  You could simply drive a
> push-pull complimentry transistor output to boost the current, but parts
> count will start rising.
>
> You may want to look at a simple zener clamped boost switcher.  Drive the
> transistor from the PWM output and adjust the duty cycle until you achive
> your maximum current without dropping under the zener voltage.  This is
> quite inefficient as the zener will be disipating most of the power at small
> loads, but may be ok for your application.
>

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.