![]() ![]() I'd just add a series fixed resistor to protect the led or to use the whole PWM scale, if that's a concern. When you want to power an LED instead you actually want power to flow into it, that's why you say "power an LED", and a resistor dissipates power, that's inevitable. Such a signal is essentially a voltage signal, little to no current should flow so power dissipation in the resistors is not really a concern. When you use high power leds their drivers usually have a PWM input anyway, and a resistor would be impractical anyway because of the amount of power it should dissipate.ĭigital potentiometers are used to attenuate an analog signal, such as a line level audio signal: you're trading some power dissipation for linearity. PWM is better because its efficiency is near unity and because it does not require any external IC if the micro can handle the led current, which is usually true. If you do not allow these cookies, you will experience reduced relevant content.The PWM solution is better under any aspect, plus the chip you linked has a quite high "full scale" resistance, $5\text\Omega$, that will lead to use less steps than available. They do not store directly personal information, but are based on uniquely identifying your browser and internet device. They may be used by Analog Devices to build a profile of your interests and show you relevant content on our site. Targeting Cookies: These cookies may be set through our site by Analog Devices and our service providers. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance. All information these cookies collect is aggregated and therefore anonymous. They help us to know which pages are the most and least popular and see how visitors move around the site. Performance Cookies: These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. If you do not allow these cookies then some or all of these services may not function properly. They may be set by us or by third party providers whose services we have added to our pages. Functional Cookies: These cookies enable the website to provide enhanced functionality and personalization. These cookies do not store any personally identifiable information. You can set your browser to block or alert you about these cookies, but some parts of the site will not then work. They are usually only set in response to actions made by you which amount to a request for services, such as setting your privacy preferences, logging in or filling in forms. Strictly Necessary Cookies: (Always Active) These cookies are necessary for the website to function and cannot be switched off in our systems. After we finish updating our website, you will be able to set your cookie preferences. Replacing the EPOT of Figure 1 with an RC network reduces both the IC count and the required number of control lines.Ī similar article appeared as a Design Idea in the Februedition of EET.Īnalog Devices is in the process of updating our website. The circuit also includes a 6.65kΩ resistor across the integrating capacitor, which reduces the 5V PWM signal to 1.25V as required by the IC's ADJ input.įigure 2. An RC time constant at least 50 times the PWM period produces a smooth average voltage across the capacitor. The average voltage at ADJ (pin 4) varies with the PWM signal and enables the IC (a current regulator for LEDs) to control the LED brightness. Simply replace the EPOT with a simple RC integrator and program the port to output a PWM signal (Figure 2). You can control each LED driver directly with a single output port. There is an alternative that reduces the number of ICs and control lines. ![]() A common brightness-control circuit for LEDs uses an electrically controlled potentiometer (EPOT) to achieve digital control of the LED brightness. For large systems, however, that approach can require many EPOTs, each requiring two control lines, or address decoding, or both.įigure 1. A common approach for achieving this adjusts an electrically controlled potentiometer (EPOT), which in turn, controls the LED driver (Figure 1). Replacing the EPOT with an RC network, however, reduces both the IC count and the required number of control lines.Ī system in which a microcontroller or programmable logic controls one or more LEDs often requires the capability of controlling LED brightness. ![]() ![]()
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