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The Microcontroller Idea Book - Jan Axelson's Lakeview Research

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Chapter 4<br />

Figure 4-6. Power supply circuit for EPROM-programming voltages.<br />

VPP: 12V to 13V<br />

VCC: 5.75V to 6.25V<br />

If you use 5%-tolerance resistors for R1 and R2, you may have to vary the value of R2 for<br />

the proper output, especially to meet the requirement for Vcc. Or, you can use a 5K<br />

potentiometer for R2 and adjust for the desired output, or use 1%-tolerance resistors for a<br />

more precise output.<br />

You can wire the LM317 circuits to your 8052-BASIC circuit board, and add terminals or<br />

jacks for connecting a 15V supply. Wire the LM317’s output to the appropriate connections<br />

in Figure 4-5.<br />

Switching Regulators<br />

A third way to generate programming voltages is to use switching regulators like those<br />

available from Maxim Semiconductor. <strong>The</strong>se can create the programming voltages from<br />

your +5V supply. For example, the MAX633 can create outputs of 6 and 12.5V from a +5V<br />

62 <strong>The</strong> <strong>Microcontroller</strong> <strong>Idea</strong> <strong>Book</strong>

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