How much is the total budget power consumption? If it is not so high,
quite some linear regulator will be able to cope with wide input 
voltage (say <=30V or even <=45V). It also looks a bit strange
for me to see MCP1700 here. Is it really safe to be used since its
maximum voltage is only 6V (or 6V5)?

I still like the idea of using a SMPS. As for simple SMPS controller,
I think they are comparable to the price of 10F204 and saves you 
the cost of programming of 10F204. For example we have an old design
using MC33063AD SO8 and it costs about US$0.3. It may even save you 
the external MOSFET Q5 and the associated driving circuits (R3, Q2, Q4,
Q3, R2, R4 and C7)if your budget current consumption from 5.5V 
is less than 500mA (I think it should be the case since MCP1700 
can only deliver 250mA, unless you have other plan for the 5V5).

Xiaofan

/**** Quoted from On-Semi Website ****/
The MC34063A Series is a monolithic control circuit containing the
primary functions required for DC-to-DC converters. These devices
consist of an internal temperature compensated reference, comparator,
controlled duty cycle oscillator with an active current limit circuit,
driver and high current output switch. This series was specifically
designed to be incorporated in Step-Down and Step-Up and
Voltage-Inverting applications with a minimum number of external
components. Refer to Application Notes AN920A/D and AN954/D
for additional design information.
* Operation from 3.0 V to 40 V Input
* Low Standby Current
* Current Limiting
* Output Switch Current to 1.5 A
* Output Voltage Adjustable
* Frequency Operation to 100 kHz
* Precision 2% Reference


-----Original Message-----
From: olin_piclist@embedinc.com [mailto:olin_piclist@embedinc.com]
Sent: Thursday, May 19, 2005 8:56 PM
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] PIC prototype board comments?


Chen Xiao Fan wrote:
> Cannot agree more with you on the power supply design. It only
> serves the purpose of demonstrating the nice use of PIC 10F
> as a SMPS controller but it can not beat a simple SMPS
> controller.

It does in price.  I've been down this route a few times and the 10F
solution has come out cheaper.  I've got similar circuits in several volume
products, and they work very nicely.

> a simple 9V supply with a 7805 will be the cheaper
> and more robust design.

Yeah, I've been hearing this a lot.  I think the cost differential is less
than people imagine, but I agree it would still be cheaper.  My main
motivation was to have flexible input voltage requirements.  It would be no
problem to specify 9V DC in and use a 7805, but would that really cost less
since the external supply would cost more?

I'm going to carefully price out a few complete solutions (wall wart and
all) and see where things come out.  How much is flexible input power
requirement worth?


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